Removal of molybdenum or tungsten or other heavy metal anions from mining wastewater can be effected by precipitation of the heavy metal anions with ferric ion, supplied preferably through addition to the wastewater of ferric sulfate. The heavy metal precipitate, so formed, is separated from the wastewater by electrolytic, dissolved air or dispersed air flotation. Such a removal process is described in copending application Ser. No. 920,259 filed June 29, 1978 in the names of the present inventor and Gopalan Ramadorai and is entitled "Process for Removing Molybdenum and Tungsten from Mining Wastewater," the contents of which application are incorporated by reference herein. Such process is also described generally in the publication entitled "Removal of Heavy Metals from Mining Tailings Wastewater by Electrocoagulation" by the present inventor and A. P. Giannini, presented at the Third Annual Conference, New Advances in Liquid-Solid Separation Technology, Separ/Expo III, at Cherry Hill, N.J., Oct. 12, 1977, the contents of said paper also being incorporated by reference herein.
The process described in the aforementioned disclosures, while teaching the separation of molybdenum or other heavy metals from the wastewater, does not, however, relate to reclamation of the heavy metal anions from the wastewater skimmings produced, or recovery of ferric ion therefrom for recycle to the wastewater treatment process. Since such skimmings contain toxic metals, care must be exercised in their disposal. Hauling such toxic materials to suitable landfill is, of course, expensive.
The present invention is related to a method for treating the wastewater skimmings produced according to the aforedescribed process and to the reclamation of the heavy metal anions present therein, as well as recovery of the ferric content of the wastewater for recycle and re-use in the wastewater treatment process. The reclaimed heavy metal values may be sold for their marketable values, while ferric sulfate produced is recycled to the wastewater treatment process.